[Spontaneous motor activity and radial-maze learning in rats neonatally treated with 6-hydroxydopamine].

6-Hydroxydopamine (6-OHDA: 35 micrograms) was intraventricularly injected twice to rat pups with desmethylimipramine pretreatment (20 mg/kg, sc) at 3 and 6 days of age in order to selectively deplete brain dopamine. At every 3 days from 7 through 31 days of age, the pups were tested for their locomotive activity in the open-field. The locomotive activity was measured by two different methods (counting the number of sections traversed and time-sampling behavioral items such as pivoting, creeping and walking). The results showed that significant increases in the activities by the both methods were produced by the treatment of 6-OHDA throughout the observation days. From 80 days of age the animals were trained 1 trial per day on radial 8-arm maze learning. Rats treated with 6-OHDA took significantly more trials to attain the learning criterion (at least 7 correct choices in the first 8 choices for 5 consecutive trials) as compared with the control animals. This retardation, however, was mainly derived from that of familiarization (habituation) to the apparatus in the beginning of the training. In conclusion, the neonatal treatments with 6-OHDA produced pronounced hyperactivity during the developmental period but little deficit in learning ability during the adult period.